I wasn't clear on my definition of "incentive." Since the loan costs nothing, paying it off early does not save interest, whereas a loan with an interest rate greater than zero, the earlier it is paid it off, the better. That's what I meant by incentive, as in "the potential to save money."
And to your point, one might argue that a 0% interest loan provides the most benefit to an individual who doesn't need it - i.e. someone who has the cash to buy outright. Say an item costs $25K and is being offered with a 0% interest loan over 5 years. One who has that amount in cash could set up a series of term deposits (or other investment product) to come to maturity in 1, 2, 3, and 4 years, paying the loan down with those funds while making some modest investment income in the process.